Cyclic fluctuation in spontaneous motor activity (CM), with a cycle time of 1-5 minutes, is a stable aspect of behavioral organization in the 3rd trimester human fetus and in other species, and is likely to regulate adaptive interactions with the environment. The mechanism of CM may be a very common one, so that understanding it would have broader significance. It also provides an opportunity to test the utility of dynamical systems theory in explaining behavioral organization. In the fetal sheep, the fetal environment can be manipulated with precision and control, behavior and physiological variables can be measured directly and accurately, and both can be done continuously during a significant portion of gestation. Three studies are proposed to advance our understanding of the prenatal development, mechanism, and functional significance of CM. Study 1 (Characterization and Development) has the following specific aims: (a) document the existence and development of CM in the fetal sheep during the last quarter of gestation, (b) determine the influence of behavioral state, (c) determine the effects of spontaneous myometrial activity, and (d) determine if increased myometrial activity accelerates CM maturation. Study 2 (Mechanism) has the following aims: (a) determine if CM is a local as well as global property of the motor system, (b) determine if descending input from the brain is necessary for CM and if there are multiple sources, (c) determine if a chaotic dynamical system might be responsible for CM, and (d) probe the properties and dynamics of CM with brief chemosensory perturbations. Study 3 (Functional Consequences) has the following aims: (a) determine if CM modulates adaptive responses to extrinsic stimulation, and (b) determine if CM influences habituation to repeated stimulation. Protocols designed as part of all 3 component projects will provide the data needed to achieve these objectives. Long term defects in neurobehavioral development constitute a major personal, emotional and economic cost to society. The knowledge obtained in these three studies will significantly increase our understanding of the intrinsic organization of fetal behavior. This information is essential for predicting the effects of acute and chronic alterations of the fetal environment on early neurobehavioral development.